The ecology of the magpie goose, Anseranas semipalmata Latham, in the Northern Territory has been studied with a view to determining its relationship to the developing rice industry on the subcoastal plains. The distribution of the geese since European settlement of Australia is discussed, and it is shown that the speoies was rapidly exterminated in the southern part of the continent, although irruptions to these regions still occur. In the Northern Territory geese confine most of their activities to the subcoastal plain but occasionally use the other habitats available to them. The birds are to some extent nomadic. In the dry season most of them concentrate on the Mary and South Alligator Rivers, and during the wet season they spread over the other rivers to breed. Movements are mainly controlled by the availability of food, water, and breeding habitat. The main foods are the seeds of swamp grasses, the blades of dry-land grasses, and the underground bulbs of spike-rush. Changes in the availability of these foods occur both seasonally and annually, and are discussed. Breeding occurs at the end of the wet season. The breeding season and the location of the colony are determined by the depth of water and the density and height of the swamp vegetation. It is concluded that the birds will not be a continuing pest of rice, but rather will be eradicated by the industry.